Settings & keep-time · Quiet Hours, pausing and schedules
What does the Power row in the popover show?
Short answer: In Smart mode only, it combines your battery level, whether you're on mains power, and whether a meeting is detected — the signals that decide if automatic work may run.
It appears only in Smart mode and combines the two signals Smart mode watches besides your activity: your battery level and whether you're on mains power, plus whether a meeting is detected.
It's there so you can see at a glance why automatic work is or isn't running. Change the thresholds in Settings → Quiet Hours.